Amazon has added Latency Based Routing to its Amazon Route 53, its distributed web service that provides DNS lookup.

As we reported when it was first released, Route 53 chooses a server for your lookup from its worldwide selection depending on where you are located for a fast response time. Without Route 53, your hosting service implements DNS, often relying on a single machine or a small cluster at a single geographical location, and without the means to configure the DNS server.

When Route 53 was launched Latency Based Routing (LBR) was one of the features that was missing for developers whose applications span multiple AWS regions. LBR means you can reduce latency for your end users by serving their requests from the region for which the network latency is lowest. This is calculated based on actual performance measurements of the different AWS regions where your application is running. Of course, for this to work you need to have instances in several AWS regions so the requests from your end-users can be routed to the region with the lowest latency.

According to a blog post by Jeff Barr, behind the scenes Amazon is constantly gathering anonymous internet latency measurements and storing them in a number of Relational Database Service instances for processing. “These measurements help us build large tables of comparative network latency from each AWS region to almost every internet network out there. They also allow us to determine which DNS resolvers those end-users generally use.”

Amazon is introducing Latency Based Routing pricing at $0.75 per million queries, for the first billion queries per month, and $0.375 per million queries for all additional queries in a given month.

The blog post says that Amazon is also making it possible to create "ALIAS" records that point to resource record sets within your own Route 53 hosted zone. These ALIAS records act as pointers or arrows in a decision tree, enabling you to compose latency based record sets, weighted record sets and multi-record record sets. These can then be used to set up sophisticated routing models, says Barr.

“By combining weighted resource record sets and an alias to a latency based record set, it's possible to have a simple "dial" determining how often latency based routing should be used at first. By starting with a small percentage and gradually increasing that percentage any risks of regional overload or poor user experience can be minimized.”

If you want to find out more about Amazon Route 53 and the Latency Based Routing feature, there’s a webinar on April 26th at 10AM PST.

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